Ballast-free ship

ABSTRACT

By adjusting the amount of air supplied from compressed-air supply piping, a seawater level in an air cushion chamber is adjusted. Accordingly, even in a case of a ballast-free ship, there is secured a function to adjust a hull equivalent to an adjusting function of a ship having ballast tanks. 
     One end of the compressed-air supply piping is opened to the air cushion chamber divided by horizontal and vertical partition plates. Below the horizontal partition plate, a current plate is disposed with a space through which seawater passes therebetween. In an air chamber provided inside a side wall, the other end of a vent pipe is provided in an opened manner at the same position in the height direction as an upper face of the current plate. One end of the vent pipe is opened at a seawater surface outside of the side wall.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a ballast-free ship in which a function of ballast tanks is performed by air cushion chambers.

2. Description of the Related Art

A ship, in particular, a cargo vessel is designed including the weight of a cargo on board etc. Therefore, when the ship is in a no cargo condition, the center of gravity of a hull goes up and the ship is likely to turn over. The draft falls, the ship rises, and the ship becomes unstable to a traverse wave and a side wind. The dead angle region is extended, which makes it difficult to recognize a small ship. The danger of a collision arises, stress strength to an external force falls, and an accident may occur. Further, the decline in propulsive efficiency is caused. In order to prevent these, ballast tanks provided in a hull are loaded with seawater, serving as a weight to stabilize the hull. Generally, the larger the ship is, the more quantities of ballast water it requires. The ballast tank capacity to the amount of tonnage of the deadweight is 30% for a container ship, 40% for a crude-oil tanker, and 80% for an LNG ship in general. The ballast water is loaded and discharged at different harbors. Because of improvement in speed of a ship, it travels between countries in a short time with living aquatic species contained in the ballast water, producing an environmental problem of disturbing ecosystem on a global scale.

In view of this problem, a ballast-free ship which is not loaded with ballast water is being studied and developed. For example, a ship as follows is proposed. That is, a ship bottom is considerably inclined in a parallel part of a hull. In this way, even when the ship is in a no cargo condition, the draft required for a safe voyage is achieved without the ship being loaded with ballast water (for example, refer to Non-patent Documents 1 and 2).

In the ballast-free ship according to Non-patent Documents 1 and 2, its vertical cross-section of the ship bottom is formed in the shape of an isosceles triangle by inclining inwardly the lower parts of the port side and the starboard side. The insufficiency of the deadweight caused thereby is compensated by increasing the hull width. As a result, the ports that the ship can call at are limited because of width restriction of canals or coastal situations. Moreover, in order to make the stern draft small, the propeller diameter is decreased by about 10% as compared to a conventional ship. Therefore, in order to compensate for the fall in propulsive efficiency, the ship's horsepower is increased, which eventually increases the amount of fuel to be used.

In the ballast-free ship according to Non-patent Document 3, a large-bore pipe is arranged from a bow to a stern in the portion of the hull below the water surface. Therefore, in a state where seawater is constantly passing through the pipe, the pipe is liable to be corroded by the seawater and the maintenance workability of the pipe is not good. Also, depending on the flow speed of the seawater passing through the pipe, aquatic species inhabit there. Thus, those aquatic species may travel between different countries in a short time. Moreover, the ratio of the pipe provided in the hull to the content volume of the hull is large, causing the gross tonnage to be small.

The ship as follows is proposed (see, for example, Patent Document 1). That is, the ship bottom is recessed. A watertight recessed portion for pooling air whose lower portion is opened is provided. A vertical partition wall and a horizontal partition wall are made to intersect perpendicularly to partition the watertight recess for air pooling. An air supply pipe in communication with an air supply unit provided in the upper part of the hull is branched at a halfway position. The lower ends of the branched air supply pipes in which air valves are provided, respectively, are opened and in communication with the respective sections. The air valve is adjusted based on the information obtained by a water surface monitor provided in the ship bottom. The amount of air of each section is adjusted by sending and discharging air to and from each section. The hull is raised above the water surface by an air layer in each section. Further, at the time of cruising, by decreasing viscous resistance, an economical cruise is achieved.

In the case of a ship having characteristics of the ship bottom structure of Patent Document 1, when supplying air, in order to prevent the ship bottom from rising above the water surface, it is necessary to monitor the water level carefully by a water level monitoring device with naked eyes. When air more than the capacity of the section is supplied from the air supply pipe, in order to discharge excessive air to the outside from a lower opening part of the section, the ship bottom is raised above the water surface. Thus, the hull loses its balance, which is extremely dangerous.

The ship as follows is proposed (see, for example, Patent Document 2). That is, a side plate is provided around the ship bottom and a recess is made inside the side plate. Alternatively, a middle flat portion of the bow and all the stern of the ship bottom is recessed as much as the height of the side plate to form a recessed portion. Partition walls are provided lengthwise and widthwise in these recessed portions to form numbers of air chambers. Each air chamber is in communication with a pipe having a check valve for compressed air. Further, an air compressor provided in the hull supplies compressed air to each air chamber.

With regard to the ship having the ship bottom structure of Patent Document 2, when air more than the capacity of each air chamber is supplied through an air supply pipe, in order to discharge excessive air to the outside from the lower opening part of the air chamber, the ship bottom is raised above the water surface and the hull loses its balance, which is very dangerous.

There is proposed an air cushion ship (see, for example, Patent Document 3) whose inventor is the same as the inventor of the present application. According to the above air cushion ship, there is provided a rear end part of a current plate in a lower portion of the partition plate with which an air cushion room is divided. A piping drainage portion for engine cooling water is extended. Of the air cushion chambers, in the air cushion chamber nearest the bow side, the piping for engine cooling water is allowed to have at least two mountain-like curved parts. An air intake pipe whose upper end is opened in the upper portion of the hull and the piping for engine cooling water are brought into communication. The air is exhausted together with the cooling water used in the air cushion chamber, and the exhausted air can be supplied to the air cushion chamber.

Any one of the ships having air cushion chambers of Patent Documents 1 to 3 does not allow its air cushion chambers to function as ballast tanks, but has ballast tanks separately. The gross tonnage is obtained by deducting a particular section (for example, ballast tanks) from all the hull content volume. The tax on deadweight or a ship is determined based on the gross tonnage. Therefore, the ship with ballast tanks therein has a problem of the tax on deadweight or the ship being high.

-   [Non-patent Document 1] Project Supported by the Nippon Foundation     Website of Japan Railroad Construction, Transport and Technology     Agency “Research and Development of Ballast-free Ship” Report on     Outline of Research Results March, 2006 Issued by Japan Ship     Technology Research Association -   [Non-patent Document 2] Website of Test Center, Shipbuilding     Research Center of Japan -   [Non-patent Document 3] Photograph by University of     Michigan/“Ecosystem is protected by ballast-free ship” at Website of     Transtex (Site management: JR Souken Information System Co., Ltd.) -   [Patent Document 1] JP-A-Sho 61 (1986)-232982 -   [Patent Document 2] JP-A-Hei 10 (1998)-100985 -   [Patent Document 3] Japanese Patent No. 3677682

SUMMARY OF THE INVENTION

The present invention is made in view of the problems of the above related arts, and its object is to provide a ship as follows. That is, the lower end of the vent pipe whose both ends are opened to an air chamber provided between an inner plate and an outer plate in the lower portion of both the right and left gunwales of the hull is opened at the same height position as the upper face of a current plate. The seawater level in each air cushion chamber is kept from becoming below the opening position of the lower end of the vent pipe. By adjusting the amount of air supply or discharge from compressed-air supply piping, adjustment in the case of rolling of the hull is performed. Thus, even in the case of a ballast-free ship, it becomes possible to perform the adjustment of the hull similar to the case of a ship having ballast tanks.

According to one aspect of the present invention, air chambers are provided in lower portions of right and left side walls of a hull. There is provided a chamber which has a flat ship bottom along a vertical centerline of the hull covering from a bow side to a stern side. With the vertical centerline of the hull being an axis of symmetry, air cushion chambers whose lower ends are opened on both the right and left sides of the chamber are provided in a recessed manner at opposing positions. Along a moving direction of the hull, vertical partition plates are provided to a bottom shell in the air cushion chamber. Two or more mutually parallel horizontal partition plates are provided vertically to the bottom shell perpendicularly to the moving direction of the hull. The air cushion chamber is partitioned by using the vertical and horizontal partition plates as partition walls. A lower edge position of the horizontal partition plate is set so that it may be located above a horizontal position of a lower edge of the vertical partition plate. At a lower position of the horizontal partition plate, a space through which seawater passes is provided so as to horizontally dispose a current plate. A lower surface of the current plate, lower edges of the right and left side walls of the hull, and an external surface position of the ship bottom of the chamber are set at the same horizontal position in the height direction. The other end of compressed-air supply piping whose one end is connected to a compressed-air supply unit for supplying and discharging compressed air to and from the partitioned air cushion chamber is allowed to be opened to and in communication with the air cushion chamber and the air chamber, respectively. Both ends of a vent pipe are opened. One end of the openings is opened at a water surface. The other end is opened at the same position as an upper end face of the current plate in the height direction in the air chamber. A seawater level in the air cushion chamber is kept from becoming below the opening position of the lower end of the vent pipe. Further, in order to equalize the air quantities in the air cushion chambers, there is achieved permeability between the air chambers and the air cushion chambers.

According to another aspect of the present invention, air chambers are provided in lower portions of right and left side walls of a hull. At a ship bottom of the hull, air cushion chambers whose lower portions are opened are provided in a recessed manner covering from a bow side to a stern side. Along a moving direction of the hull, vertical partition plates are provided to a bottom shell in the air cushion chamber. Two or more mutually parallel horizontal partition plates are provided vertically to the bottom shell perpendicularly to the moving direction of the hull. The air cushion chamber is partitioned by using the vertical and horizontal partition plates as partition walls. A lower edge position of the horizontal partition plate is set so that it may be located above a horizontal position of a lower edge of the vertical partition plate. At a lower position of the horizontal partition plate, a space through which seawater passes is provided so as to horizontally dispose a current plate. An undersurface of the current plate and lower edges of the right and left side walls of the hull are set at the same horizontal position in the height direction. The other end of compressed-air supply piping whose one end is connected to a compressed-air supply unit for supplying and discharging compressed air to and from the partitioned air cushion chamber is allowed to be opened to and in communication with the air cushion chamber and the air chamber, respectively. Both ends of a vent pipe are opened. One end of the openings is opened at a water surface. The other end is opened at the same position as an upper end face of the current plate in the height direction in the air chamber. A seawater level in the air cushion chamber is kept from becoming below the opening position of the lower end of the vent pipe. Further, in order to equalize the air quantities in the air cushion chambers, there is achieved permeability between the air chambers and the air cushion chambers.

According to the present invention, there are provided the vent pipes in the air chambers disposed in the lower portions of the right and left side walls of the hull. Further, the lower end of the vent pipe is opened at the same position as the upper face of the current plate in the height direction. Therefore, the seawater level in the air cushion chamber is kept from becoming below the opening position of the lower end of the vent pipe, which prevents the center of gravity of the hull from rising. Moreover, by adjusting the amount of air supplied from the compressed-air supply piping or the amount of air exhausted, rolling of the hull etc. are prevented. Thus, even in the case of a ballast-free ship, it becomes possible to adjust the balance of the hull as in the case of a ship having ballast tanks. When excessive compressed air is supplied from the compressed-air supply unit or the hull is rolled, the position of the lower opening of the vent pipe in communication with the air chamber is raised above the seawater level. In such a case, air instantly enters through the lower opening of the vent pipe and is exhausted from the upper opening of the vent pipe through the vent pipe. Therefore, a position of the lower end of the vent pipe becomes the lowest limit of seawater level in the air cushion chamber. Since the hull does not rise abnormally, the center of gravity of the hull does not go up, which prevents the dangerous situations such as the hull losing its balance and the accident being caused.

In the ballast-free ship according to the present invention, drag reduction is performed to the seawater flowing on the current plate while cruising. The seawater, taken into the lower portion of the air cushion chamber, of the harbor that the ship leaves is discharged from the air cushion chamber in a direction opposite to the moving direction when the ship starts cruising. Also, in the initial stage of the cruising, the aquatic species of the harbor which the ship leaves are also discharged from the air cushion chamber. That is, the aquatic species of the sea area of the harbor that the ship, has stayed in the air cushion chamber are instantly discharged backward together with seawater from the air cushion chamber because of the resistance of the ship bottom by the propulsive movement of the ship in the initial stage of the cruising. Thus, the aquatic species cannot stay inside the air cushion chamber and, therefore, can not be transported, not causing situations such as disturbing the ecosystem.

In the ballast-free ship according to the present invention, the seawater in the air cushion chamber is constantly discharged in a direction opposite to the moving direction and is replaced. By supplying the compressed air from the compressed-air supply unit, it is possible to prevent the seawater from adhering to the bottom shell inside the air cushion chamber, which prevents the ship bottom from being corroded.

The gross tonnage is expressed by a hull content volume. In the case of the present ballast-free ship, the air cushion chambers are provided outside the hull. Accordingly, they are not counted when computing the gross tonnage. Therefore, by building a ballast-free ship having a larger hull content volume, living space and volume of the hold for the cargo can be made larger, and the deadweight can be made larger. To be specific, the hull content volume can be made larger by the volume of the recessed air cushion chambers, which greatly improves the living environment for the ship crews and deadweight.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view illustrating a principal part of a ballast-free ship (First embodiment);

FIG. 2 is an enlarged vertical cross-section along a width direction of a hull illustrating the principal part of the ballast-free ship (First embodiment);

FIG. 3 is a cutaway right side view showing the principal part (First embodiment);

FIG. 4 is a sectional view showing the relation between a current plate and seawater while cruising (First embodiment);

FIG. 5 is a partially cutaway bottom view (First embodiment);

FIG. 6 is an enlarged vertical cross-section along a width direction of a hull illustrating a principal part of a ballast-free ship (Second embodiment); and

FIG. 7 is a cutaway right side view showing the principal part of FIG. 6 (Second embodiment).

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The other end of the vent pipe whose both ends are opened is opened at the same horizontal position as the upper face of the current plate in the height position. Thus, the seawater level of the seawater which enters the air cushion chamber is kept from becoming below the upper face of the current plate, and the center of gravity of the hull is kept from rising above a fixed position. Therefore, even in the case of a bad weather, rolling etc. of the hull are prevented and the accidents such as overturning of the ship can be avoided. Moreover, depending on a no cargo condition or deadweight, compressed air is supplied or discharged and the balance of the hull is adjusted. Therefore, dangerous situations such as rolling of the ship and overturning are avoided. Further, adhesion of seawater to the bottom shell of the air cushion chamber is prevented and the bottom shell is prevented from being corroded. Moreover, it is made possible to easily view the interior of the air cushion chamber at the dock from the lower portion of the hull. Therefore, as compared to a conventional ballast ship, maintenance workability is remarkably raised. Further, by paying attention to the fact that the gross tonnage is a content volume of the hull, the bottom shell of the air cushion chamber is recessed. Thus, the total volume of the air cushion chamber is not included in the gross tonnage, allowing the content volume of the hull to be increased by the total volume of the air cushion chambers.

First Embodiment

With reference to FIGS. 1 to 5, a ballast-free ship of a first embodiment will be explained. FIG. 1 is a plan view illustrating a principal part of a ballast-free ship, FIG. 2 is an enlarged vertical cross-section along a width direction of a hull illustrating the principal part of the ballast-free ship, FIG. 3 is a cutaway right side view showing the principal part, FIG. 4 is a sectional view showing the relation between a current plate and the flow of seawater while cruising, and FIG. 5 is a partially cutaway bottom view. In FIGS. 1 to 5, at the ship bottom part of a hull 1, there is provided an air cushion chamber surrounded by two side walls 2 of the hull 1, a bow seal, and a stern seal. The lower part of the air cushion chamber is opened. The bottom of the air cushion chamber is recessed and its vertical cross-section is an inverted concave. As shown in FIG. 2, the side wall 2 is made of sheet steel. Further, the side wall 2 includes: a flat face which configures a gunwale; and an outer plate of a bilge continuously extending from the flat face and being inwardly curved. An inner plate 3 is provided inside the side wall 2. An air chamber 4 is formed between the side wall 2 and the inner plate 3. The air chamber 4 includes a space surrounded by the side wall 2, the inner plate 3, and a first side plate 5. Between the side wall 2 and the inner plate 3, there are provided upper and lower space portions separated by a second side plate 6 and a third side plate 7. The third side plate 7 is provided continuously with a main deck 8.

In the ship bottom of the hull 1, there is provided a chamber 9 having a predetermined breadth along a longitudinal centerline of the hull from the bow side to the stern side. The chamber 9 is a space surrounded watertight by a flat ship bottom 10 and walls 11 being perpendicular to the flat ship bottom 10 and erected respectively from right and left side edges of the ship bottom 10. The chamber 9 can be used for various purposes such as a cargo bay or a ship crews' living space. The flat ship bottom 10 is provided in the same plane where the lower edge (lower edge of the outer plate of the bilge) of the side wall 2 is at the same position in the height direction.

On the bottom shell 12 of the hull 1, there are vertically provided vertical partition plates 13, along the moving direction of the hull 1, perpendicularly to the bottom shell 12, and up to the position corresponding to the lower edge (lower edge of the outer plate of the bilge) of the right and left side walls 2 of the hull 1. Moreover, on the bottom shell 12, there are vertically provided two or more mutually parallel horizontal partition plates 14, at right angles with the moving direction of the hull 1, perpendicularly to the bottom shell 12 and up to the halfway position in the height direction of the right and left side walls 2. The intervals of the horizontal partition plates 14 vary according to the types of ships. The air cushion chamber 15 is partitioned by the vertical partition plates 13 and horizontal partition plates 14. There are provided air circulation holes 16, respectively, in the partition walls comprising the vertical partition plates 13 and the horizontal partition plates 14 of partitioned air cushion chambers 15, respectively. The positions in the height direction of the air circulation holes 16 in the vertical partition plate 13 and the horizontal partition plate 14 are set above the positions where lower ends of vent pipes 17 to be described later are opened.

Along the horizontal partition plate 14, a current plate 18 is provided in the lower portion of the horizontal partition plate 14. The current plate 18 is attached to the lower edge of the vertical partition plate 13 so that it may be in parallel with the bottom shell 12 provided horizontally. To be specific, at a position corresponding to a lower part of the horizontal partition plate 14 in the lower end of the vertical partition plate 13, there is integrally attached to the vertical partition plate 13 the current plate 18 which has a predetermined front and back width, which is remarkably long in the horizontal direction, and which is rectangle as viewed in a plane such that it is in parallel with the bottom shell 12. There are provided, at the same horizontal position in the height direction, the undersurface of the vertical partition plate 13, lower edges of the right and left side walls of the hull, and a ship bottom 10 of the chamber 9 such that they are positioned in the same plane.

Air compressors 19 are provided in the hull 1. The air compressor 19 is connected to and in communication with a main pipe of compressed-air supply piping 20 through an air compressor chamber and an air tank. Known means is used for compressed-air supply means. For example, means described in Japanese Patent No. 3077032 is used.

The main pipe of the compressed-air supply piping 20 is branched. Pipes of the branched compressed-air supply piping 20 have valves therein and are opened to and in communication with each air cushion chamber 15 and each air chamber 4, respectively. The valve provided in the branch pipe of the compressed-air supply piping 20 detects the amount of air charged, seawater level, etc. in each air cushion chamber 15. Thus, the valve can be controlled to be opened and closed by a control unit according to the information obtained. A valve is provided in an exhaust pipe 21. One end thereof is opened to the side wall 2, and the other end joins the main pipe of the compressed-air supply piping 20. The valve provided in the exhaust pipe 21 detects the amount of air charged, seawater level, etc. in each air cushion chamber 15. The valve can be controlled to be opened and closed by a control unit according to the information obtained.

Both ends of the vent pipe 17 are opened. The vent pipe 17 passes through first and second side plates 5 and 6. One end of the vent pipe 17 is opened at the sea surface in the external surface of the side wall 2. The other end of the vent pipe 17 is opened at the same position as the upper face of the current plate 18 in the height direction in the air chamber 4.

Now, operations of the present invention will be explained. When the hull 1 is in a no cargo condition, the compressed air in the air cushion chamber 15 presses down the seawater surface. As a result, the hull 1 goes up and the center of gravity of the hull 1 tends to rise. When the center of gravity of the hull 1 rises, the hull 1 loses its balance and the ship may turn over. Therefore, according to the first embodiment, when the hull 1 is in the no cargo condition, the drive of the air compressor 19 is suspended. Then, the valve in the branch pipe of the compressed-air supply piping 20 and the valve disposed in the exhaust pipe 21 are opened. Air in the air cushion chamber 15 is exhausted from the exhaust pipe 21 through the branch pipe of the compression-air supply piping 20 to the above the seawater surface. When the air in the air cushion chamber 15 is exhausted, the seawater level in the air cushion chamber 15 rises, and the hull 1 does not go up. In order that the seawater surface may not come in contact with the bottom shell 12, a control unit (not shown) controls and adjusts the amount of compressed air to be discharged in relation to the seawater level.

When the hull 1 is loaded, the hull 1 tends to descend because of the weight of a cargo. The valve in the branch pipe of the compressed-air supply piping 20 is opened. With the valve disposed in the exhaust pipe 21 being closed, the air compressor 19 is driven to supply compressed air through a branch pipe of the compressed-air supply piping 20 into the air cushion chamber 15. The seawater surface in the air cushion chamber 15 is pressed down by the air pressure of the compressed air, and the hull 1 goes up. When the position of the seawater surface in the air cushion chamber 15 becomes the same as the upper face of the current plate 18 in the height direction, even if the supply of the compressed air is continued, the compressed air to be supplied enters an opening of the other end of the vent pipe 17, and is exhausted into the atmosphere above the seawater surface from the one end opening of the vent pipe 17. Even if the compressed air is excessively supplied to the air cushion chamber 15, the seawater level in the air cushion chamber 15 does not become below the upper face of the current plate 18. Therefore, the hull 1 does not turn over by oversupply of the compressed air.

The other ends of the vent pipes 17 are opened, in the air chambers 4 which includes a right chamber and a left chamber relative to the chamber 9, at the same position as the upper faces of the current plates 18, respectively, in the height direction. When the hull 1 loses its right-and-left balance, an opening of the other end of the vent pipe 17 provided in one raised air chamber 4 of the right and left air chambers 4 rises above the seawater surface. In such a case, the valve in the branch pipe of the compressed-air supply piping 20 on the raised side is closed. The air with which the air cushion chamber 15 on the raised side is filled enters the opening of the other end of the vent pipe 17, and is exhausted from an opening of one end of the vent pipe 17 into atmosphere above the seawater surface. The opening of the other end of the vent pipe 17 on the raised side holds the state of being constantly in contact with the seawater surface.

On the other hand, into the air cushion chambers 15 on the descended side, compressed air is supplied from the compressed-air supply piping 20 by the drive of the air compressor 19. As a result, the air cushion chambers 15 rise, which allows the seawater levels in the right and left air cushion chambers 15 to be uniform. Thus, even when the hull 1 has lost its right-and-left balance, the seawater level does not become below the opening of the other end of the vent pipe 17, allowing the balance to be kept.

Moreover, the vent pipe 17 is opened at the same position as the upper face of the current plate 18 in the height direction. Therefore, the seawater level in the height direction does not become below the upper face of the current plate 18 in the air cushion chamber 15. Arrows in FIG. 4 show the flow of seawater during cruising. The sea water flows on the current plate 18 during cruising. Therefore, the seawater inside the air cushion chamber 15 is not stored in the air cushion chamber 15 but is constantly replaced. Because of the water flow caused by the ship cruising, aquatic species in the seawater are discharged, together with the seawater, backward from the air cushion chamber 15. Thus, they are not transported to other harbors, not disturbing the ecosystem.

Second Embodiment

With reference to FIGS. 6 and 7, a second embodiment will be described. In the description to follow, like reference numerals are used to designate like portions as in FIGS. 1 to 5 for simplicity. At the ship bottom of the hull 1, there is provided an air cushion chamber 15 whose vertical cross-section, in which the ship bottom is recessed, is in the shape of an inverted concave. The side wall 2 includes: a flat face which configures a gunwale; and an outer plate of a bilge which extends continuously from the flat face and is curved inwardly. An inner plate 3 is provided inside the side wall 2, and an air chamber 4 is provided between the side wall 2 and the inner plate 3. The air chamber 4 includes a space surrounded by the side wall 2, the inner plate 3, and a first side plate 5. Between the side wall 2 and the inner plate 3, there are provided two space portions separated by a second side plate 6 and a third side plate 7. The third side plate 7 is provided continuously with a main deck 8. In the bottom shell 12 of the hull 1, there is vertically provided a vertical partition plate 13, along the moving direction of the hull 1, perpendicularly to the bottom shell 12 and up to the position corresponding to a lower edge (lower edge of the outer plate of the bilge) of the right and left side walls 2 of the hull 1. Further, to the bottom shell 12, there are vertically provided two or more mutually parallel horizontal partition plates 14 perpendicularly to the moving direction of the hull 1, at right angles with the bottom shell 12 and up to the halfway position in the height direction of the right and left side walls 2. The air cushion chamber 15 is partitioned by the vertical and horizontal partition plates 13 and 14. Along the horizontal partition plate 14, there is provided a current plate 18 at the position corresponding to the lower part of the horizontal partition plate 14 at the lower end of the vertical partition plate 13. The current plate 18 is attached to the lower edge of the vertical partition plate 13 so that it may have a spatial relationship of being in parallel to the bottom shell 12 formed horizontally. In the vertical partition plate 13 and the horizontal partition plate 14, there are formed air circulation holes 16. No air circulation hole is formed in a vertical partition plate 13, among vertical partition plates 13, provided on a vertical centerline of the hull 1.

Further, the present invention includes an embodiment wherein, among the vertical partition plates 13, in a vertical plate 13 provided on the vertical centerline of the hull 1, air circulation holes 18 are formed. The compressed-air supply piping 20 is branched. Branch pipes of the compressed-air supply piping 20 with valves therein are opened to and in communication with each air cushion chamber 15 and each air chamber 4, respectively. The valve disposed in the branch pipe of the compressed-air supply piping 20 detects the amount of air charged, seawater level, etc. in the air cushion chamber 15. The valve is controlled to be opened and closed by a control unit according to the information obtained.

A valve is provided in an exhaust pipe 21. One end thereof is opened to the side wall 2 and the other end joins a main pipe of the compressed-air supply piping 20. The valve disposed in the exhaust pipe 21 detects the amount of air charged, seawater level, etc. in each air cushion chamber 15. The valve can be controlled to be opened or closed by a control unit according to the information obtained.

Both ends of the vent pipe 17 are opened. The vent pipe 17 passes through a first side plate 5 and a second side plate 6. One end of the vent pipe 17 is opened at the seawater surface on the external side of the side wall 2. The other end of the vent pipe 17 is opened at the same position as the upper face of the current plate 18 in the height direction in the air chamber 4.

Next, operations will be explained. When the hull 1 is in a no cargo condition, the compressed air in the air cushion chamber 15 presses down the seawater surface. As a result, the hull 1 rises, and the center of gravity of the hull 1 tends to go up. When the center of gravity of the hull 1 goes up, the hull 1 loses its balance, which may cause the ship to turn over. Therefore, according to the first embodiment, when the hull 1 is in the no cargo condition, the drive of the air compressor 19 is suspended. Then, the valve in the branch pipe of the compressed-air supply piping 20 and the valve in the exhaust pipe 21 are opened. The air in the air cushion chamber 15 is exhausted into the atmosphere above the seawater surface from the exhaust pipe 21 through the branch pipe of the compressed-air supply piping 20. When the air in the air cushion chamber 15 is exhausted, the seawater level in the air cushion chamber 15 rises, and the hull 1 does not go up. In order that the seawater surface may not come in contact with the bottom shell 12, a control unit (not shown) controls and adjusts the exhaust amount of the compressed air in connection with the seawater level.

If the hull 1 is loaded, the hull 1 tends to descend by the weight of a cargo. With the valve disposed in the branch pipe of the compressed-air supply piping 20 opened and the valve disposed in the exhaust pipe 21 closed, the air compressor 19 is driven. Further, the compressed air is supplied into the air cushion chamber 15 through the branch pipe of the compressed-air supply piping 20. The seawater level in the air cushion chamber 15 is lowered by the air pressure of the compressed air, and the hull 1 rises. When the seawater level in the air cushion chamber 15 is at the same position in the height direction as the upper face of the current plate 18, even if the compressed air is supplied further, the compressed air to be supplied enters an opening of the other end of the vent pipe 17, and is exhausted into the atmosphere above the seawater surface from the opening of one end of the vent pipe 17. Even if the compressed air is supplied to the air cushion chamber 15 successively, the position of the seawater level in the air cushion chamber 15 does not become below the upper face of the current plate 18. Therefore, even when the compressed air is supplied excessively, the hull 1 does not turn over.

The other end of the vent pipe 17 is opened at the same position in the height direction as the upper face of the current plate 18, respectively, in the right and left air chambers 4. When the hull 1 loses its right-and-left balance and an opening of the other end of the vent pipe 17 provided in the raised air chamber 4 of the right and left air chambers 4 is above the seawater level, the valve in the branch pipe of the compressed-air supply piping 20 on the raised side is closed. The air with which the air cushion chamber 15 on the raised side is filled enters the opening of the other end of the vent pipe 17 on the raised side and is exhausted above the seawater surface from an opening of one end of the vent pipe 17. The opening of the other end of the vent pipe 17 on the raised side is allowed to be constantly in contact with the seawater surface. On the other hand, by driving the air compressor 19, compressed air is supplied from the compressed-air supply piping 20 into the air cushion chamber 15 on the descended side, and the air cushion chamber 15 is raised. With the vertical partition plate 13 disposed on a vertical centerline of the hull 1 as a center, seawater levels in right and left air cushion chambers 15 are allowed to be uniform. Thus, even when the hull 1 loses its right-and-left balance, without the seawater level being below the opening of the other end of the vent pipe 17, the balance can be kept. Moreover, the vent pipe 17 is opened at the same position in the height direction as the upper face of the current plate 18. As a result, with the position of the upper face of the current plate 18 being a lower limit, the seawater level of the air cushion chamber 15 does not become lower than that. The ship advances while the seawater flowing on the upper surface of the current plate 18. Therefore, the seawater in the air cushion chamber 15 is not stored but is constantly replaced. Further, aquatic species in the air cushion chamber 15 are discharged backward of the hull together with the seawater. Therefore, the aquatic species are discharged, together with sea water, in the sea area near the place where they have flown in. Thus, they are not transported to another harbor which, as a result, does not lead to disturbing the ecosystem. 

1. A ballast-free ship, comprising air chambers provided in lower portions of right and left side walls of a hull; a chamber which has a flat ship bottom along a vertical centerline of the hull covering a bow side to a stern side and, with the vertical centerline of the hull being an axis of symmetry; air cushion chambers whose lower ends are opened on both the right and left sides of the chamber and provided in a recessed manner at opposing positions; vertical partition plates provided along a moving direction of the hull to a bottom shell in the air cushion chamber; two or more mutually parallel horizontal partition plates provided vertically to the bottom shell perpendicularly to the moving direction of the hull, wherein the air cushion chamber is partitioned by using the vertical and horizontal partition plates as partition walls, a lower edge position of the horizontal partition plate is set so that it may be located above a horizontal position of a lower edge of the vertical partition plate and, at a lower position of the horizontal partition plate, a space through which seawater passes is provided so as to horizontally dispose a current plate; wherein a lower surface of the current plate, lower edges of the right and left side walls of the hull, and an external surface position of the ship bottom of the chamber are set at the same horizontal position in the height direction; a compressed-air supply piping having first and second ends, wherein said first end is connected to a compressed-air supply unit for supplying and discharging compressed air to and from the partitioned air cushion chamber, wherein said second end opened to and in communication with the air cushion chamber or the air chamber; a vent pipe having a first and second open end, said first end opened above the surface of water, the second end is opened at the same position as an upper end face of the current plane in the height direction in the air chamber; wherein the air chambers are communicated with the air cushion chambers so that a seawater level in the air cushion chamber is kept from becoming below the opening position of the second end of the vent pipe and the air quantities in the air cushion chambers is equalized.
 2. A ballast-free ship, comprising air chambers provided in lower portions of right and left side walls of a hull; air cushion chambers whose lower portions are opened and provided at a ship bottom of the hull in a recessed manner covering from a bow side to a stern side; vertical partition plates provided along a moving direction of the hull to a bottom shell in the air cushion chamber; two or more mutually parallel horizontal partition plates provided vertically to the bottom shell perpendicularly to the moving direction of the hull, wherein the air cushion chamber is partitioned by using the vertical and horizontal partition plates as partition walls, a lower edge position of the horizontal partition plate is set so that it may be located above a horizontal position of a lower edge of the vertical partition plate and, at a lower position of the horizontal partition plate, a space through which seawater passes is provided so as to horizontally dispose a current plate; wherein an undersurface of the current plate and lower edges of the right and left side walls of the hull are set at the same horizontal position in the height direction; a compressed-air supply piping having first and second ends, wherein said first end is connected to a compressed-air supply unit for supplying and discharging compressed air to and from the partitioned air cushion chamber, wherein said second end is alternately opened to and in communication with the air cushion chamber or the air chamber; a vent pipe having a first and second open end, said first end opened above the surface of water, the second end is opened at the same position as an upper end face of the current plate in the height direction in the air chamber; and wherein the air chambers are communicated with the air cushion chambers so that a seawater level in the air cushion chamber is kept from becoming below the opening position of the second end of the vent pipe and the air quantities in the air cushion chambers is equalized. 